1. Field of the Invention
This invention relates to a stable liquid preparation of complex vitamin for internal use, and more specifically to a liquid preparation of complex vitamin for internal use, which remains stable even when stored for a long period at room temperature.
2. Description of the Related Art
Like vitamin B.sub.6, vitamin B.sub.1 and vitamin B.sub.12 are closely associated with nervous functions and are effective for the improvement of neuroses such as neuralgia, arthralgia, peripheral neuritis and peripheral paralysis. A variety of tablets and capsules added with these vitamins are therefore available on the market.
As a dosage form, a liquid preparation generally features that compared with such tablets and capsules, the liquid preparation is more readily absorbed in the body and is easier to take. Nonetheless, no stable liquid preparation containing both vitamin B.sub.1 and vitamin B.sub.12 has been available on the market. This is attributed to the poor storage stability of a liquid preparation containing both of them.
As causes for the poor storage stability of the liquid preparation added with both vitamin B.sub.1 and vitamin B.sub.12, it is known that the stable pH ranges of these vitamins in an aqueous solution are different, i.e., pH 2-4 for vitamin B.sub.1 and pH 4.5-5 for vitamin B.sub.12 and also that SR-containing decomposition products of vitamin B.sub.1 extremely lower the stability of vitamin B.sub.12.
Further, sucrose is generally used as a sweetening agent in liquid preparations for internal use. Sucrose may however lower the stability of vitamin B.sub.1 and vitamin B.sub.12, depending on its concentration and the pH. Liquid preparations for internal use are also added with a corrigent, a flavoring agent, a buffer agent, a preservative and the like. These additives may also give adverse effects on the stability, thereby making it more difficult to formulate a liquid preparation for internal use, which contains vitamin B.sub.1 and vitamin B.sub.12.